"In the 1931-1932 period, Hückel published three long papers on aromatic and unsaturated molecules, the first providing a quantum theoretical description of benzene (1931, 1932). This was his habilitation thesis leading to the venia legendi (right to teach) in theoretical physics at the Technische Hochschule Stuttgart. In this paper Hückel gave two descriptions of benzene: his first method, which eventually came to be known as the valence bond method, and a second, which involved the application of molecular orbital methods. Hückel believed that the experimental data gave him good reasons for preferring the second approach, which was utilized by John Lennard-Jones, Hund, and Robert Mulliken. This second approach is widely known as the HMO method (Hückels molecular orbital method)." (DSB).